1. Field of the Invention
The present invention relates to liquid crystal display devices. More particularly, the present invention relates to electrically birefringence (ECB) mode transmissive type liquid crystal display devices.
2. Discussion of Related Art
A liquid crystal display (LCD) device may be classified as a twisted nematic (TN) type, an electrically birefringence (ECB) type, and an optically compensated birefringence (OCB) type according to an operating mode of the LCD device. An LCD device may be further classified as a transmissive LCD device and a reflective LCD device according to a kind of a light source employed by the LCD device. Transmissive type LCD devices may use an internal light source such as a backlight to display images, and reflective type LCD devices may use an external light source such as natural sunlight to display images.
LCD devices having advantages of both transmissive LCD devices and reflective LCD devices are desired. Transflective LCD devices are being researched as LCD devices having advantages of both the transmissive and reflective type LCD devices. Transflective LCD devices generally include an ECB mode liquid crystal panel.
FIG. 1 illustrates a schematic cross-sectional view showing a conventional transflective type LCD device.
As illustrated in FIG. 1, the conventional transflective LCD device may include an electrically controlled birefringence (hereinafter referred to as “ECB”) mode liquid crystal panel 100, a first retardation film 110, a first polarizing plate 120, a second retardation film 130, and a second polarizing plate 140. The ECB mode liquid crystal panel 100 may drive one or more liquid crystal cells, and may include first and second substrates 102 and 104, first and second orientation films 103 and 105, which may be provided on opposing inner surfaces of the first and second substrates 102 and 104, respectively, and liquid crystal 107 between the first and second substrates 102 and 104. The first retardation film 110 may be formed on an outer surface of the first substrate 102. The first polarizing plate 120 may be formed on an outer surface of the first retardation film 110. The second retardation film 130 may be formed on an outer surface of the second substrate 104. The second polarizing plate 140 may be formed on an outer surface of the second retardation film 130.
The first and second retardation films 110 and 130 may function to change a polarized state of light. For example, a λ/4 retardation plate or a λ/2 retardation plate may be used as the first and second retardation films 110 and 130. A λ/4 retardation plate may change a line polarization into a circle polarization. A λ/2 retardation plate may rotate a line polarization or a circle polarization at a predetermined angle. A light transmittance axis of the first polarizing plate 120 may form an angle of 90° with respect to a light transmittance axis of the second polarizing plate 140.
A backlight (not shown) may be arranged on an outer surface of the second polarizing plate 140, e.g., a lower side of the second polarizing plate 140.
In conventional ECB mode transflective LCD devices, as illustrated in FIG. 1, retardation films 120, 130 and polarizing plates 120, 140 are arranged on both upper and lower sides of the ECB mode liquid crystal panel 100, thus, increasing a thickness of such LCD devices. ECB mode liquid crystal panels may generally be employed in transflective type LCD devices.
To embody a transmissive type LCD device using an ECB mode liquid crystal panel with only polarizing plates formed on the liquid crystal panel, retardation state(s) may remain in the ECB mode liquid crystal panel, and a dark state may be difficult and/or impossible to attain.